Syringodermatales ord. nov. and Syringoderma floridana sp. nov. (Phaeophyceae)

Abstract

Syringoderma floridana sp. nov. (Phaeophyceae), a monostromatic species from Florida, has a heteromorphic life history in which zoospores from unilocular sporangia are scarcely motile and the gametophyte is reduced to two cells, both of which differentiate as biflagellate, morphologically similar gametes. Syringoderma abyssicola is interpreted as having similar four-celled gametophytes which develop within the unilocular sporangium and release four biflagellate isogametes. Evidence for heteromorphic sporophytes and gametophytes in all four known species of Syringoderma, and the presence of several vegetative characters of Syringoderma differing from those of both the Dictyotales and Sphacelariales, support the placement of Syringoderma in a separate order Syringoderrnatales ord. nov., containing the single monogeneric family Syringodermataceae fam. nov.